1. Field of the Invention
The present invention relates to a calculation method and a calculation apparatus using a computer. The present invention also relates to a program embodied on a computer readable medium that causes a computer to execute the calculation method.
2. Description of the Related Art
Various kinds of medical images such as X-ray images, RI images, CT (Computed Tomography) images, ultrasonic images, and MRI (Magnetic Resonance Imaging) images have been in wide use in the field of medicine. Furthermore, radiation image reading/recording systems (CR; Computed Radiography) using stimulable phosphor are also well known. Stimulable phosphor stores a portion of energy of radiation irradiated thereon, and emits a phosphorescent light in accordance with the stored radiation energy upon exposure to an excitation light such as a visible light or a laser beam. In a radiation image reading/recording system, radiation image information of a subject such as a human body is recorded in a stimulable phosphor sheet and the sheet is scanned with an excitation light such as a laser beam to cause the sheet to emit a phosphorescent light. The phosphorescent light is photoelectrically read to obtain an image signal.
In such a system, image processing such as tone processing and frequency processing is carried out on the image signal and a visible diagnostic image of an excellent diagnostic value (that is, an image easy to read) is recorded on a photosensitive material (such as a film), based on the image signal after the image processing. Alternatively, the image signal is displayed on a display device such as a CRT after being recorded temporarily in a recording medium. In this manner, the radiation image is reproduced and provided for diagnosis. Various kinds of image processing such as tone processing, frequency enhancement processing for emphasizing soft-tissue, bones, the mediastinum, and the like, soft-tissue or bone display processing using energy subtraction, and enlargement/reduction processing can be carried out as the image processing for reproduction of radiation image information regarding a human body.
In such image processing, operations including division, such as filtering processing and interpolation processing, is carried out a large number of times (for each pixel, for example). Therefore, a large amount of calculation is carried out. Especially, since medical images that need to be of high quality have a large amount of data, the amount of calculation also becomes extremely large.
However, a computing speed for the image processing described above depends on the performance capability of a computer inside an image processing apparatus. Therefore, in order to speed up the image processing, the computing speed of computers have been increased.
Unfortunately, only increasing the computing speed of a computer does not fundamentally solve the problem of operation speed, because the content of the image processing also becomes more complex for better processing in accordance with an increase in the computing speed.
Therefore, in order to speed up the image processing, an efficiency of the calculations carried out in the computer needs to be improved, in addition to increasing the computing speed.
A computing speed by a computer is generally much slower for division than for addition or subtraction. Therefore, in the image processing that often uses division repeatedly, the computing speed of division greatly influences an operation time necessary for the image processing. Consequently, fast division in a computer can lead to an increase in the image processing speed.